The present invention relates to a method, and also to apparatus, for cooling and scanning infrared devices, particularly infrared detector assemblies.
Infrared detector assemblies, used for thermal imaging or non-imagining purposes, have to be cooled to a very low temperature corresponding to that of liquid nitrogen. Cryogenic coolers operating according to the Stirling thermodynamic cycle are commonly used for this purpose. Such coolers include a compressor section having a piston (commonly called the compressor-piston) and an expander section also having a piston (commonly called the displacer). The outer surface of the expander section is cooled (the latter being called the "cold finger"), and the infrared detector assembly is mounted on that surface. In the conventional Stirling cooler, the displacer (expander-piston) is reciprocated with respect to the outer housing of the cold finger. When such Stirling coolers are used for cooling infrared detector assemblies, the infrared detectors are scanned by mechanical scanning devices, such as rotating mirrors either along one axis (line scanner) or along two axes (two-dimensional scanner).